Filtration of solid particles from a flowing gas is frequently desired and often necessary in a variety of industrial processes. Many chemical, refining and related processes require removal of particulate matter from a gas stream to clean the gas, to extract the particulate matter, or both. When a gas is to be discharged to the atmosphere, particle removal is both desirable and necessary to prevent air pollution, to maintain site and equipment cleanliness and to provide suitable conditions for workers. This invention, adaptable to many gas filtration applications, is particularly useful for cleaning dust-laden air discharged during the drilling of holes into the earth.
Many machines for drilling holes into the earth use compressed air to blow dirt and rock cuttings from the hole. Typically, the compressed air flows through a drill rod or pipe to orifices in the cutting tool where it is discharged into the drilled hole at atmospheric pressure and flows in large volume back through the drilled hole to the atmosphere, carrying particulate dust and larger cutting particles to the surface. Unless that air is filtered at the surface, the dust and cuttings cause a very dirty work site and wide ranging air pollution. Seepage water carried to the surface with the cuttings causes an added problem of clogging the surface of many filter mediums with mud and causing a breakdown of others, such as paper filter media.
Large volumes of air heavily laden with dust and cuttings must be continuously treated while drilling progresses, preferably without interruption. Filters capable of handling these large flow volumes have not been available in physical sizes small enough to mount on the drilling machines. The drilling machines vary in size from small crawler tractor and truck mounted portable units to large semi-portable truck, trailer or platform mounted drilling rigs.
Fabric bag filters of the type used for mechanical barrier separation of particles in many industrial plant processes have been tried and found to not be practical for these applications. For sufficient bag surface to filter a given air flow volume per unit time, a multi-bag filter unit of a physical size as large or larger than the drilling machine would be required. Bag filters have other limitations such as rapid wear, mud clogging in wet drilling conditions and continuous cleaning difficulties.
One approach to air filtration for these applications uses an array of pleated paper filter elements within a compartmentalized housing. The pleated paper elements are of the type commonly used for engine air intake filtration on stationary engines and off-the-road vehicle engines. A pleated paper element can provide a filter surface area equivalent to a bag filter element five or more times physically larger. However, the prior art, as particularly set forth in U.S. Pat. No. 4,218,227, is based on deration of the air flow velocity through the paper elements; the overall result being that the physical size of a multiple paper element filter unit of the prior art is less than that of a multi-bag filter unit of comparable air volume handling capacity, but the reduction in physical size then only amounts to about fifty percent because the paper elements are not utilized at full rated capacity.
This physical size reduction is significant but still results in a filter unit too large for easy portability and too large for drilling rig mounting in most cases. This adaptation of pleated paper filter elements has other limitations in that high pressure, 90 to 100 PSIG, compressed air is needed for element cleaning; water droplets, if present in the air stream, are carried into the paper elements causelement deterioration, and large cutting particles can clog the required mechanical discharge valve. Because a large number of filter elements are needed for even a small drill application, a relatively complex arrangement of backcleaning pulse air valve controls is needed. Often alternating current electricity for operating these controls and the discharge valve motor is not available on a drilling rig.
It is, therefore, an object of this invention to provide a new and improved filter for separation of particulate matter from a flowing gas stream. It is a further object to provide an effective particle filter of smaller physical size than prior art filters for handling a relatively large gas flow volume. Another object is to provide such a filter capable of effectively filtering large flow volumes of air heavily laden with dust and cutting particles and small enough in size to mount on a portable drilling machine. Additionally, it is an object to provide such a filter that is operable without electric current or high pressure compressed air. Other objects and advantages of the invention will be apparent in the following summary and description.